For example, Japanese Patent Application Laid-Open Publication No. 2014-195147 (Patent Document 1) describes a scheme in which each of a plurality of line cards receives monitoring frames from two redundant management cards and selects one of these frames to transmit it to an outside of a device in a chassis-type network relay device. Also, ITU-T G.8032/Y.1344 (February 2012) (Non-Patent Document 1) describes a ring protocol of a ring network based on ITU-T G.8032.